Dependence of the polarizability of the $Cu_4O_8$ cluster on the doping, the weight of the oxygen-hole state, and the excitation gaps in the three-band Hubbard model

Ramasesha, S and Rao, CNR
(1991)
Dependence of the polarizability of the $Cu_4O_8$ cluster on the doping, the weight of the oxygen-hole state, and the excitation gaps in the three-band Hubbard model.
In: Physical Review B, 44
(13).
pp. 7046-7050.

Abstract

We have obtained the model exact static polarizability of the $Cu_4O_8$ cluster within the three-band Hubbard model for different doping levels. The excitation gaps as well as the weight of the $O^-$ (oxygen-hole) state in the ground-state wave function have been exactly computed. The parameters of the model are varied to alter the excitation gaps as well as the weight of the $O^-$ state in order to examine the dependence of the polarizability on these quantities. The $Cu_4O_8$ cluster is highly polarizable, the polarizability increasing with the doping level. The polarizability is large when the excitation gap is charge-transfer-like and increases with the decreasing gaps; it also increases markedly with the increase in the weight of the $O^-$ state. Experimentally, the $T_c$ in the cuprates is highest for the range of the weight of $O^-$ for which the lattice is highly polarizable.